Carrier Aggregation inter eNB activation

ABSTRACT

A method for deciding on the activation of carrier aggregation across first and second base stations of a cellular network for delivering a service to a mobile terminal is provided. The decision is made on the basis of a combination of a plurality of parameters. One parameter is associated with a performance of the cellular network. One parameter is associated with a Quality of Service requirement of the service. One parameter is associated with a state of the mobile terminal and/or a subscriber associated with the mobile terminal. One parameter is associated with a radio link between the mobile terminal and the first base station and/or second base station.

TECHNICAL FIELD OF THE INVENTION

The invention concerns a method for deciding on the activation ofcarrier aggregation on first and second base stations of a cellularnetwork for delivering a service to a mobile terminal and a networkentity configured to operate accordingly.

BACKGROUND TO THE INVENTION

A conventional cellular network comprises a plurality of base stations,each base station transmitting to one or more mobile terminals (eachreferred to as a respective User Equipment or UE) using at least onerespective carrier. In particular, the Third Generation PartnershipProject (3GPP) have specified Long Term Evolution (LTE) architectures,in which each base station (called an eNodeB or eNB in this context)transmits downlink signals to UEs using one or more Orthogonal FrequencyDivision Multiplexed (OFDM) carriers. Each carrier occupies a frequencybandwidth and therefore defines a data rate capacity for deliveringservices to the UEs.

Carrier aggregation allows a UE to be served by multiple differentcarriers at the same time, allowing flexible allocation of datatransmission to those carriers. This may increase the data rate that canbe communicated between the network and the UE, for instance allowing aUE to reach a high peak data rate by being provided with access to morespectrum. Although originally only standardised for aggregation betweentwo carriers on the same eNB (intra-eNB carrier aggregation), in 3GPPRelease 12, aggregation between two carriers on different eNBs is beingstandardised (inter-eNB carrier aggregation). The specification work isintended to define the way and amount of information to be exchanged(signalling mechanisms) so that aggregation is successfully achieved.Inter-eNB carrier aggregation is most relevant between a macro cell anda small cell and it would typically be used where the coverage areas ofthe base stations intersect.

Referring first to FIG. 1, there is shown a schematic diagram of a partof a network architecture to permit inter-eNB carrier aggregation. AMaster eNB 20 and a Secondary eNB 30 each communicate with a UE 60 usinga respective Uu (air) interface 65. An Mobility Management Entity (MME)70 interfaces with a Home Subscriber Server (HSS) 80 and the MME 70communicates with the Master eNB 20 and the Secondary eNB 30 overrespective S1 interfaces 75. Moreover, the Master eNB 20 and theSecondary eNB 30 can communicate with each other over an Xn interface50. The Xn interface allows the Master eNB 20 and the Secondary eNB 30to exchange information and for the Master eNB 20 to control theSecondary eNB 30 if required. The Secondary eNB 30 may also makeautonomous decisions. Typically (although not necessarily), the MastereNB 20 is a macro cell and the Secondary eNB 30 is a small cell. Onegeneralised approach for inter-eNB carrier aggregation is discussed inWO-2012/136256. Thus, a carrier may be aggregated at the UE 60, suchthat Master Base Station (MeNB) 20 transmits carrier frequency X to theUE and Secondary Base Station (SeNB) 30 transmits carrier frequency Y tothe UE. The additional, aggregated carrier is referred to as a SecondaryCell (SCell).

3GPP Technical Report (TR) 36.842 v12.0.0 discusses particulartechniques for implementing inter-eNB carrier aggregation. Referring toFIGS. 2A and 2B, there are illustrated techniques discussed in thisdocument that have been standardised by 3GPP based on the networkarchitecture shown in FIG. 1. Where the same features are indicated asin FIG. 1, identical reference numerals have been used.

FIG. 2A shows a first technique (referred to as “Alternative 1A” in 3GPPTR 36.842 v12.0.0). Service data 10 is provided to the Master eNB 20 andthe Secondary eNB 30 from the MME 70 over the respective S1 interfaces75. This service data 10 comprises two bearers (for example, voice anddata respectively). The bearers are split: one bearer is communicated tothe UE 60 through the Master eNB 20; and the other bearer iscommunicated to the UE 60 through the Secondary eNB 30. Each eNB hasrespective Packet Data Convergence Protocol (PDCP), Radio Link Control(RLC) and Media Access Control (MAC) layers for processing the bearers.

FIG. 2B depicts a second technique (referred to as “Alternative 3C” in3GPP TR 36.842 v12.0.0). In this architecture, a single bearer of theservice data 10 can be split between the Master eNB 20 and the SecondaryeNB 30. In the illustration shown, the Master eNB 20 receives twobearers and one bearer is split at the PDCP layer between it and theSecondary eNB 30. The portion of the bearer for transmission by theSecondary eNB 30 is communicated from the Master eNB 20 to the SecondaryeNB 30 over the Xn interface 50. This portion of the bearer is thenprocessed at the RLC and MAC layers by the Secondary eNB 30 fortransmission to the UE 60.

Some approaches exist to address a number of issues relating toInter-eNB carrier aggregation. For example, WO-2013/143051 discussespower saving techniques for inter-eNB carrier aggregation andUS-2014/0078989 discusses how inter-eNB carrier aggregation can be setup.

Carrier aggregation between an eNB and a Node B has previously beenconsidered. WO 2012/171587 describes an apparatus for deciding if datato be transmitted to a UE should transmitted by a slave base station ofa second radio access technology (RAT). The decision is based on anavailability indication from the slave base station that may comprise,for example, a transmission time delay, an available capacity or aquality of service.

Nevertheless, many significant challenges still remain in theimplementation of inter-eNB carrier aggregation, such as when toimplement it, which implementation technique to use and how to manageresources between the base stations.

SUMMARY OF THE INVENTION

Against this background, there is provided a method for deciding on theactivation of carrier aggregation on first and second base stations of acellular network for delivering a service to a mobile terminal inaccordance with claim 1, a computer program in line with claim 14 and anetwork entity of a cellular network as defined by claim 15. It shouldbe understood that this method is part of a telecommunications networkcomprising: at least one UE; a radio access network (RAN); and corenetwork (CN). Preferably, the first and second base stations areconfigured for use within a Long Term Evolution network architecture.Other preferred features are disclosed with reference to the claims andin the description below.

The decision on activating carrier aggregation in an inter-base station(inter-eNB, when the base stations are LTE-based) is therefore madebased on one or more parameters that affect both the quality of theservice provided to the mobile terminal using carrier aggregation andthe additional resources required to implement carrier aggregation. Byusing these parameters, an assessment can be made whether inter-basestation carrier aggregation is worthwhile and therefore improveefficiency, power consumption and quality of service. Such an assessmentmay not be as relevant for intra-base station carrier aggregation, wherethe additional resources required are more centralised and notnecessarily as significant.

In particular, the parameters may include: a latency requirement of theservice; a minimum bit rate requirement of the service; a mobility stateof the mobile terminal; a quality of service state of the mobileterminal (such as a maximum delay tolerance for the mobile terminal); abattery state of the mobile terminal; a transmission power back-off ofthe mobile terminal state; and a parameter based on an assessment of achange in throughput due to carrier aggregation activation relative to achange in transmission overheads due to carrier aggregation activation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be put into practice in a number of ways, andpreferred embodiments will now be described by way of example only andwith reference to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of a part of a network architecture topermit inter-eNB carrier aggregation;

FIGS. 2A and 2B illustrate techniques for implementing inter-eNB carrieraggregation based on the network architecture shown in FIG. 1;

FIG. 3 shows an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on various variables, in accordancewith a first embodiment;

FIG. 4 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a first variable shown in FIG. 3;

FIG. 5 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a second variable shown in FIG.3;

FIG. 6 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a third variable shown in FIG. 3;

FIG. 7 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a fourth variable shown in FIG.3;

FIG. 8 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a fifth variable shown in FIG. 3;

FIG. 9 depicts an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on a sixth variable shown in FIG. 3;

FIG. 10 illustrates a flow chart for selecting a technique forimplementing inter-eNB carrier aggregation, in accordance with a secondembodiment;

FIG. 11 shows a flow chart for flow control of inter-eNB carrieraggregation data traffic, in accordance with a third embodiment; and

FIG. 12 shows a flow chart for configuring scheduling for inter-eNBcarrier aggregation data traffic, in accordance with a fourthembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A number of specific embodiments will be discussed below, with referenceto a system based on 3GPP LTE Advanced. However, it should not beunderstood that the invention is limited to such systems. When the termeNB is used below, this may be substituted for a more general basestation and likewise, other network entities may be replaced with ageneralised entity carrying out a similar function in a differentnetwork architecture.

The first embodiment relates to determination of whether to activatecarrier aggregation. Then, the second embodiment concerns the selectionof a technique for carrier aggregation when activated. Finally, thethird and fourth embodiments address resource allocation when carrieraggregation is activated.

Carrier Aggregation Activation Decision

Referring first to FIG. 3, there is shown an example flow chart fordeciding whether to implement inter-eNB carrier aggregation based onvarious variables. When configuring carrier aggregation, it has beenfound that various parameters have an impact on the final userperformance. Therefore, the decision to implement carrier aggregationshould take at least one and preferably multiple such parameters intoaccount. The parameters found to be most relevant comprise: QoS (such aslatency); a UE state, such as mobility or battery usage; and a linkstate, such as overhead levels or power backoff. These parameters aretherefore provided as inputs to a decision process, which takes place atthe Master eNB (MeNB). The MeNB is typically a macro cell. Using theprovided parameters, the MeNB makes an adequate estimate on the likelyperformance improvements or degradations due to setting up carrieraggregation for a given UE. This decision process is shown in FIG. 3.Optionally, the default position is that carrier aggregation is notenabled.

Nevertheless, the process need not take place at the MeNB, Secondary eNB(SeNB) or even at another eNB. It could take place at another networkentity or at each relevant mobile terminal. Moreover, not all of theparameters discussed above need be used. More generally, this can beunderstood as a method for deciding on the activation of carrieraggregation across first and second base stations of a cellular networkfor delivering a service to a mobile terminal.

In particular, the decision may be on the basis of at least oneparameter associated with one or more of: a performance of the cellularnetwork; a Quality of Service requirement of the service; a state of themobile terminal and/or a subscriber associated with the mobile terminal;and a radio link between the mobile terminal and the first base stationand/or second base station.

As an alternative, the decision may be on the basis of a combination ofa plurality of parameters, at least one parameter being associated witha performance of the cellular network, at least one parameter beingassociated with a Quality of Service requirement of the service, atleast one parameter being associated with a state of the mobile terminaland/or a subscriber associated with the mobile terminal and, at leastone parameter being associated with a radio link between the mobileterminal and the first base station and/or second base station.

These more general definitions of the parameters noted above, but thespecific parameters will be discussed in more detail below.

The decision may establish whether the benefit of the increased datathroughput provided by carrier aggregation outweighs the increasedresources required to implement it. In this context, carrier aggregationacross the first and second base stations may be understood asaggregating a carrier (or a plurality of carriers) of the first basestation and a carrier (or a plurality of carriers) of the second basestation in respect of the mobile terminal. The parameters arebeneficially considered as part of the signalling process to the mobileterminal. The step of deciding on the activation of carrier aggregationis optionally based on a plurality of these parameters. By monitoringthese parameters, it is possible for the mobility management entity(MME), respective base station or UE to determine if carrier aggregationor a sole carrier from the MeNB or SeNB is appropriate for the UE.Optionally, the method may further comprise activation or deactivationof carrier aggregation in response to the step of deciding.

The method may be implemented by means of a computer program, which willcause the steps to be carried out when operated by a processor (or otherlogic). The computer program may be stored on a computer readablemedium. In another aspect, there may be provided a network entity of acellular network, configured to set an activation state for carrieraggregation based on a decision made in accordance with the method asdescribed herein. The network entity may have structural features (suchas respective components, modules or parts) configured to provide thefunctionality associated with any of the steps discussed herein. Thenetwork entity is optionally the first or second base station, themobile terminal, part of another known network entity or a new networkentity.

The input data may come from different points of the network, such as:the UE; MeNB; SeNB; scheduler information at the MeNB; or the corenetwork (for example subscription data). If the MeNB decides to setupcarrier aggregation, then another algorithm is run to decide when tostop it based on any change in the input information. If carrieraggregation is not activated, the scheduler at the MeNB dynamicallymonitors the input data to decide when is best to set up carrieraggregation or not.

In general, configuration of carrier aggregation is a network decisionbased on UE support for the functionality (which may include secondaryband support and carrier aggregation combinations supported). If the UEis able to perform carrier aggregation, the scheduler of the network candecide to activate the Secondary Cell (SCell) and send“Activation/Deactivation MAC control element” to the UE, which inaccordance with 3GPP TS 36.321 v.12.2.0:

“if the UE receives an Activation/Deactivation MAC control element inthis TTI activating the SCell, the UE shall in the TTI according to thetiming . . . :

activate the SCell; i.e. apply normal SCell operation including:

-   -   SRS transmissions on the SCell;    -   CQI/PMI/RUPTI reporting for the SCell;    -   PDCCH monitoring on the SCell;    -   PDCCH monitoring for the SCell.

start or restart the sCellDeactivationTimer associated with the SCell .. . ” 3GPP TS 36.331 v.12.1.0 section 5.3.3 sets out a procedure for RRCconnection establishment with multiple purposes, one of which is theconfiguring or releasing of an SCell. This procedure is also used tomodify an RRC connection, for example to establish, modify or releaseresource blocks (RBs), to perform handover, to setup, modify or releasemeasurements and to add, modify or release SCells. As part of theprocedure, NAS dedicated information may be transferred from E-UTRAN tothe UE.

The mechanisms by which the network will decide when and how it is bestto enable carrier aggregation across eNBs will now be described. Theaggregation across eNBs is subject to certain conditions which may bespecific to that scenario and may differ from the normal intra-eNBcarrier aggregation scenario.

A first parameter for consideration is QoS, specifically latency.Referring next to FIG. 4, there is depicted an example flow chart fordeciding whether to implement inter-eNB carrier aggregation based onthis variable. The threshold is typically a fixed or static value set bythe network at the Operations Support System (OSS) for example andapplies throughout the whole network when inter-site carrier aggregationis possible.

In a small cell scenario the architecture of the network may imply anon-ideal backhaul (such as a non-fibre backhaul) particularly for theXn interface. This may add certain latency into the transmissionsaffecting the real user performance. This may consequentially requirebuffering of a considerable amount of information. In this case,configuring carrier aggregation may not be optimum, irrespective of theradio conditions.

More generally, the at least one parameter associated with theperformance of the cellular network may comprise an indication oflatency for communication between network entities of the cellularnetwork (for example between the first and second base stations). Then,the method may further comprise deciding to activate carrier aggregationif the indication of latency is less than a threshold value.

Another parameter for consideration relates to the QoS of the servicebeing provided, especially latency. Referring next to FIG. 5, there isdepicted an example flow chart for deciding whether to implementinter-eNB carrier aggregation based on this variable. There may beservices that require low latency. Carrier aggregation may bedeactivated to provider lower latency and better customer experience forsuch services. Such services can for example comprise telemetry, radiocontrol (such as drones), remote surgery. The QoS requirements mayinclude at times high throughput and low latency. At other times,carrier aggregation may already be configured for some purposes (such assending video streams) while low latency is not key. Then, carrieraggregation is deactivated if the device needs to perform a task in realtime or the network asks for deactivation.

These type of services, or dedicated devices shall avoid configuringcarrier aggregation when latency may be impacted. These devices can beidentified by the eNB based on subscription data from the HSS throughMME nodes, or through a UE category signalled (in an as yet undefinedway) by the UE to the eNB. Such a UE category already exists (forexample for machine-to-machine type UEs) but is not used for thepurposes to identify UEs for low latency.

The tolerance to delay (or intolerance) is normally based on thecombined information from the subscription and UE category, which may berelated. If the UE is non-delay tolerant (for example surgery equipment,or drone device) but all data associated with it is delay-tolerant, theMeNB may decide to set up carrier aggregation. If there is part of thedata that is non-delay tolerant, for instance associated totele-commands that must be executed in real time, then the MeNB willdeactivate carrier aggregation.

This can more generally be understood as when the at least one parameterassociated with the Quality of Service requirement of the servicecomprises one or more of: a latency requirement of the service; and aminimum bit rate requirement of the service. The latency requirement ofthe service may (in part or entirely) be determined by a latencyrequirement associated with the mobile terminal (UE). The methodoptionally further comprises: deciding to activate carrier aggregationif the latency requirement of the service is at least a threshold delaytolerance level. Additionally or alternatively, the method may furthercomprise: deciding to deactivate carrier aggregation if the latencyrequirement of the service is less than a threshold delay tolerancelevel (which may be the same or different to the activation thresholdnoted above).

Further parameters for consideration may relate to a state of thesubscriber and/or mobile terminal. In general terms, the at least oneparameter associated with a state of the mobile terminal may compriseone or more of: a mobility state; a quality of service state; a batterystate; and a transmission power back-off state. One quality of servicestate of the mobile terminal may relate to service latency requirements,as discussed above.

Another particular mobile terminal QoS parameter of interest may relateto its mobility (that is, whether and how it is moving within thenetwork). Referring now to FIG. 6, there is depicted an example flowchart for deciding whether to implement inter-eNB carrier aggregationbased on this parameter.

If a UE is not fast-moving, it may be optimum to configure a Scell forit. The use of carrier aggregation in small cell scenario ensures thatUEs typically remain connected to the macro cell along its path whenmoving across small cells. In this way, a UE will minimize servicedisruption and will configure a Scell along its movement.

However, it may also be true that situations where this handling of UEsmay not be optimum. For example, a UE camping in the macro network maymove sufficiently fast so that carrier aggregation configuration andreconfiguration may not be optimum. In these cases, the optimumbehaviour may be to limit the UE to single carrier (macro cell)operation. This may avoid the configuration and reconfigurationmechanisms, saving battery, overload in the network and providing asmoother experience.

There are multiple ways to identify these users, which may comprise:Doppler information from uplink signal; counter of small cells camped ina certain period of time; connection time in a given small cell;location information, for example from a Global Navigation SatelliteSystem (GNSS), such as GPS, Galileo, BeiDou or similar.

As indicated above, there are several sources of information regardingthe mobility of a given UE and those can be combined at the MeNB (orother network entity) to take an informed decision on the nomadismcharacteristics of a given UE. If that nomadism value is over athreshold, carrier aggregation will not be configured. This thresholdvalue can be computed as a weighted summation of: a) Doppler data (andrelated speed), b) GPS data (and related speed) if available; and c) acounter of small cells per specified time period (for instance 5minutes). This can be expressed as:

Mobility_thr=weighted_Σ{avg(speed from Doppler in UL reports from UE,speed from GPS),#small_cells/Xmin}

More generally, it may be understood that the parameter associated witha mobility state is advantageously based on one or more of: Dopplerinformation from a mobile terminal transmission (received at the firstbase station and/or second base station); a rate of handover betweenbase stations for the mobile terminal; a time duration of attachment ofthe mobile terminal to a base station; and a location for the mobileterminal (for example by a GNSS). The quality of service state for themobile terminal optionally indicates a maximum delay tolerance for themobile terminal. Then, the method may further comprise deciding toactivate carrier aggregation if the maximum delay tolerance for themobile terminal is at least a threshold delay tolerance level.Additionally or alternatively, the method may comprise deciding todeactivate carrier aggregation if the maximum delay tolerance for themobile terminal is less than a threshold delay tolerance level (whichmay be the same or different to the activation threshold). In someembodiments, the parameter associated with a mobility state indicateswhether the mobile terminal is nomadic. In this case, the method mayfurther comprise deciding to activate carrier aggregation if the mobileterminal is indicated to be nomadic.

Overheads are a further parameter for consideration. Implementingcarrier aggregations causes increased overheads, particularly in termsof RRC reconfigurations. In some cases, the additional quantity ofoverheads due to carrier aggregation may impact significantly on theadditional available throughput that may be achieved as a consequence.In other words, configuring a Scell may not be optimum due to theoverheads that CA requires, from a service point of view. In such cases,it is expected that single carrier operation will provide a betterexperience. Overheads for carrier aggregation in a small cell deploymentmay be (significantly) larger than for an intra-eNB carrier aggregationscenario.

Referring now to FIG. 7, there is depicted an example flow chart fordeciding whether to implement inter-eNB carrier aggregation in view ofthis parameter. One possible measure of the overheads may use the numberof RRC reconfigurations. For carrier aggregation, RRC reconfigurationswill consist primarily of secondary cell addition, removal and change.In contrast with a mobility parameter, as noted above, the number of RRCreconfigurations may relate to the network configuration and not onlythe movement of the UE. A threshold for the maximum number of RRCreconfigurations could be applied. This could be based on either themeasured number of RRC reconfigurations, or an approach to predict thenumber of RRC reconfigurations could be used.

More generally, the at least one parameter associated with a performanceof the cellular network may comprise a parameter based on an assessmentof a change in throughput due to carrier aggregation activation relativeto a change in transmission overheads due to carrier aggregationactivation. Then, the method may further comprise deciding to activatecarrier aggregation if the assessment indicates an increase inthroughput due to carrier aggregation activation relative to a change intransmission overheads due to carrier aggregation activation. This maybe in comparison to the throughput when carrier aggregation is notactivated. Additionally or alternatively, the method may furthercomprise deciding to deactivate carrier aggregation if the assessmentindicates an increase throughput due to carrier aggregation activationwhen compared to a change in transmission overheads due to carrieraggregation activation is less than a threshold value.

Carrier aggregation may have significant power requirements, which maybe disadvantageous for a battery-powered mobile terminal. Hence, it maynot be desirable to activate carrier aggregation from the userperspective, if the remaining battery resource is limited. The decisionto activate or deactivate carrier aggregation would then be made (atleast in part) by the mobile terminal, unless this information is fedback to the network. In principle, this information is not available tothe network, but such information may optionally be provided for it tobe used by the network in making a centralised decision.

Referring now to FIG. 8, there is depicted an example flow chart fordeciding whether to implement inter-eNB carrier aggregation based onthis parameter. It will be seen that this flow chart considers twooptions:

-   -   1) the UE proactively reports the remaining battery capacity to        the network; and    -   2) the UE does not report UE battery capacity data.

In option 1), the network can proactively take an informed decision andnot activate carrier aggregation for a given UE, if the battery levelremaining is below a given threshold. This threshold is preferablystatic and may be around 10% for example. In option 2), the UE does notreport any data to the network, so the decision of setting carrieraggregation or not is ratified by the UE, ultimately based on thebattery conditions. In this case, we assume that the UE is mandated toindicate this reason to the network (for instance, in the appropriateRRC signalling message).

In a general sense, the method may further comprise receiving theparameter associated with the battery state at the cellular network fromthe mobile terminal. Then, the method may further comprise deciding toactivate carrier aggregation if the parameter associated with thebattery state indicates that the battery power level is at least a firstthreshold level and/or deciding not to activate carrier aggregation ifthe parameter associated with the battery state indicates that thebattery power level is less than a second threshold level. The firstthreshold level may be the same as the second threshold level or theymay be different (for instance, the second threshold level may be higheror lower than the first threshold level).

In some scenarios where carrier aggregation is performed across specificfrequency bands, certain restrictions in terms of transmission power mayapply. In such cases (especially where the different bands belong todifferent network entities), the impact of power back-off may be largerdue to the physical separation of the eNBs. In this case it is expectedthat a minimum carrier aggregation performance may be ensured by 3GPPprotocols (3GPP TS 36.321 MAC protocol and 3GPP TS 36.101 UE RFrequirements), so that it is possible to avoid carrier aggregation whenthe radio conditions shaped by the power back-off do not result inoptimum performance. However, further flexibility may be provided at thescheduler, so that it is left for the network to decide if powerback-off or its level is allowed or not, so that observed performance isnot degraded. Referring to FIG. 9, there is depicted an example flowchart for deciding whether to implement inter-eNB carrier aggregationbased on this variable.

The MeNB receives the required power back-off from UE and calculates anuplink path loss (that is, a coverage reduction). The MeNB can thencompare this coverage reduction to a static or configurable value whichcan depend on other inputs. These other inputs may depend on what otherbands are present. If another carrier aggregation configuration acrossother bands may not result in unreasonable power back-off, then the MeNBwill schedule the UE on that new configuration.

More generally, the transmission power back-off state may indicate atransmission power back-off associated with carrier aggregationactivation. Then, the method may further comprise assessing a throughputparameter for carrier aggregation activation based on the indicatedtransmission power back-off. The method may further comprise deciding toactivate carrier aggregation if the assessed throughput parameter is atleast a threshold level.

Each of the criteria discussed above may be considered individually, buta combination of these criteria is preferably considered, as indicatedby FIG. 3. In particular, it is not necessary for all criteria to be metto activate carrier aggregation. For example, a threshold could beapplied on the number of criteria that are met, for example at leastthree out of five criteria need to be met to activate carrieraggregation. Additionally or alternatively, some criteria could beprioritised over others. For instance, carrier aggregation is not usedif the latency requirements are not met, independently of all othercriteria. As another alternative, a weighted measure of the criteriacould be used. For example, the weighted sum of the ratios of eachcriterion to its threshold value could be used, as indicated by theformula (where w₁, w₂, w₃, etc represent weight values):

weighted_metric=w ₁*(latency_actual/latency_threshold)+w ₂*(overhead_actual/overhead_threshold)+w ₃*( . . . ) etc.

An alternative formula may replace each of the ratios by a 1 if thecriteria meets the respective threshold and by a 0 if not. In any ofthese approaches, carrier aggregation is then not activated if theweighted metric is at least a threshold level.

In general terms, the step of deciding on the activation of carrieraggregation may be based on a weighted measure of a plurality of theparameters. In particular, the step of deciding may comprise deciding toactivate carrier aggregation if the weighted measure is at least athreshold. Alternatively (or possibly in combination with anotherapproach), the step of deciding may comprise deciding to activatecarrier aggregation if one or more specific parameters from theplurality of parameters Any combination of specific features may beprovided from any of the aspects discussed above, even if thatcombination is not explicitly disclosed. Moreover, any part orcombination of parts of this aspect may be combined with any otheraspect discussed herein.

Carrier Aggregation Mode Selection

The techniques for implementing inter-eNB carrier aggregation that havebeen standardised by 3GPP have been discussed above with reference toFIGS. 2A and 2B. The architecture shown in FIG. 2A will be referenced asArchitecture 1A below and the architecture shown in FIG. 2B will bereferenced as Architecture 3C below, for the sake of convenience.

It should be noted that Architecture 1A essentially uses both basestations as separate cells, with an S1 interface terminating at theSeNB. In contrast, Architecture 3C facilitates a split of the bearersacross both eNBs with the S1 interface terminating in the MeNB. Ittherefore relies on a close connection between the macro base stationand small base station (although this may be generalised to any two basestations).

Moreover, it is further observed that Architecture 1A may only be usefulin a scenario where the service is provided with at least two differentbearers. Architecture 3C may require a flow control mechanism todetermine which data should be transmitted by the MeNB and which shouldbe transmitted by the SeNB. In addition, to enable optimised schedulingdecisions, some coordination may be required between the scheduler inthe MeNB and SeNB. The process of sending data over the Xn interface(flow control) introduces additional latency, and some services can beaffected by this.

Both architectures have advantages and disadvantages. The optimal choiceof architecture may depend on a number of factors. It has been assumedthat only architecture will be implemented by a network operator.However, a more beneficial approach is considered to enable botharchitectures and to implement a mechanism for dynamically selecting thebest architecture. Both architectures would be supported in the networkand the UE. Switching between the architectures need not be highlydynamic. Most likely, the architecture would be chosen at callestablishment, and then only change if different services are used.

In general terms, this can be understood as a method for selecting amode of service delivery to a mobile terminal using carrier aggregationacross first and second base stations of a cellular network. This mayinclude set up at initialisation and/or dynamic reconfiguration.Preferably, the selecting is based on one or more of: a parameter of theservice; and a parameter of the network architecture. The first andsecond base stations are preferably configured for use within a LongTerm Evolution network architecture. In particular embodiments, theselecting may be from a set of modes comprising: a first mode, in whichthe first base station uses a first carrier to deliver a first bearer ofthe service to the mobile terminal and the second base station uses asecond carrier to deliver a second bearer of the service to the mobileterminal; and a second mode, in which the first base station uses afirst carrier to deliver a first portion of a bearer of the service tothe mobile terminal and the second base station uses a second carrier todeliver a second portion of the bearer of the service to the mobileterminal. In both modes, there may be more than one or two bearers. Themodes only relate to the division of at least one bearer between thebase stations. Other modes may be possible.

In particular, the selection may advantageously be based on one or moreof the following criteria:

-   -   latency requirements of service (if the service being used        requires low latency, then architecture 1A may be a better        choice than 3C);    -   number of bearers used by the UE (Architecture 1A may have the        most benefit when two different bearers are used, as both        bearers can be transmitted over different cells); and    -   Performance of network links (for architecture 3C, data to and        from the small cell will be transmitted over the Xn interface,        whereas for 1A it will go over the S1 interface between the        small cell and the core network; if these interfaces are        physically separate and/or independent and one of them is        congested, while the other one is not, then it makes sense to        use the uncongested interface).

Referring now to FIG. 10, there is illustrated a flow chart forselecting a technique for implementing inter-eNB carrier aggregation.This decision making process is based on the criteria noted above.

More generally, the parameter of the service may comprise a number ofbearers of the service. Then, the step of selecting advantageouslycomprises selecting the second mode (that is, Architecture 3C) when theservice consists of (that is, only has) one bearer. If there aremultiple bearers, then the first or second modes can be employed.

In some embodiments, the parameter of the service comprises a quality ofservice requirement, for example indicating a maximum delay tolerance ofthe service. Then, the step of selecting may comprise selecting thefirst mode when the maximum delay tolerance of the service is less thana threshold level. Preferably, the step of selecting comprises:selecting on the basis on the number of bearers of the service; andsubsequently selecting on the basis of the quality of servicerequirement. Thus, the selection based on the quality of servicerequirement may typically be performed dependent on the result of theselection based on the number of bearers of the service.

In the preferred embodiment, the parameter of the network architecturecomprises an indication of congestion across at least one interface ofthe network architecture, for example an interface between the first andsecond base stations (such as the Xn interface) and/or an interfacebetween the first and/or second base station and another network entity(such as the MME, through the S1 interface). Then, the step of selectingmay comprise selecting the first mode when the indication of congestionis at least a threshold level. Additionally or alternatively, the stepof selecting may comprise selecting the second mode when the indicationof congestion is less than the threshold level. Optionally, the step ofselecting comprises: selecting on the basis of the quality of servicerequirement; and subsequently selecting on the basis of the indicationof congestion. Thus, the selection based on the indication of congestionmay typically be performed dependent on the result of the selectionbased on the quality of service requirement. In some embodiments, theselection based on the indication of congestion may typically beperformed subsequently to (and optionally based on) the selection basedon the number of bearers of the service.

The method may be implemented by means of a computer program, which willcause the steps to be carried out when operated by a processor (or otherlogic). The computer program may be stored on a computer readablemedium. In another aspect, there may be provided a network entity of acellular network, configured to select a mode of service delivery to amobile terminal using carrier aggregation across first and second basestations of the cellular network in accordance with the method asdescribed herein. The network entity may have structural features (suchas respective components, modules or parts) configured to provide thefunctionality associated with any of the steps discussed herein. Thenetwork entity is optionally the first or second base station, themobile terminal, part of another known network entity or a new networkentity.

Any combination of specific features may be provided from any of theaspects discussed above, even if that combination is not explicitlydisclosed. Moreover, any part or combination of parts of this aspect maybe combined with any other aspect discussed herein.

Resource Allocation for Carrier Aggregation

Intra-eNB carrier aggregation assumes a single entity or scheduler thatis located in a Baseband Unit (BBU) at the Base Station that can handlethe multiple carriers being aggregated. However, this is not possiblefor inter-eNB carrier aggregation, since each base station is likely tohave its own scheduler and/or BBU.

Different equipment manufacturers (vendors) use different forms ofresource allocation, in the form of scheduling and flow controlalgorithms, in their eNBs. Consider a UE supporting inter-eNB carrieraggregation (which will be referred to here as a “Rel-12” UE, inter-eNBcarrier aggregation being standardised in 3GPP LTE Release 12, asopposed to a “Rel-8” UE that does not support carrier aggregation) andconnected to two different eNBs on two different component carriers. A‘Rel-8’ UE is a UE that does not support carrier aggregation, but anypre-Rel-12 UE will not support inter-eNB carrier aggregation. If the twoeNBs are from the same vendor, then they would normally use the samescheduling algorithm or at least have a high degree of collaborationbetween their schedulers. However, if the two eNBs are from differentvendors then there is a risk of highly inefficient data scheduling tothe UE performing inter-eNB carrier aggregation for a number of reasons.

1. The two eNBs will normally have different scheduling algorithms,which would be optimizing different functions. In an extreme case, onescheduler algorithm might use a “round-robin” algorithm that guaranteesan equal share of the resources to the UEs disregarding channelconditions while the other scheduler may use a “max C/I” algorithm thattries to give most of the resources to UEs that have the best channelconditions. This would result in a non-efficient or non-optimalscheduling for the Rel12-UEs since they are scheduled with two differentscheduling algorithms on the two carriers of the two eNBs.

2. Some fairness should be guaranteed between Rel-8 UEs and Rel-12 UEs.Assuming a Rel-8 UE with access to only one carrier has the same chanceto be scheduled as a Rel-12 UE having access to N aggregated carriers.Then, the Rel-12 UE would get N times the resources of those allocatedto the Rel-8 UE. Remedying this imbalance may involve the exchange ofsome information between the eNBs about the resources used by Rel-12 UEson each carrier to guarantee some fairness to Rel-8 UEs. This problemcould exist in eNBs from the same vendor, but it could be more severe ina multi-vendor scenario.

It is proposed to have a mechanism for resource allocation, particularlyin the form of flow control and scheduling, for base stations to solvethe above mentioned issues, for example. In general terms, this can beunderstood as a method for managing service delivery to at least onemobile terminal using carrier aggregation across first and second basestations of a cellular network. For example, this may be achieved bymanagement of resources and/or data in connection with the second basestation.

The method may comprise determining, at a network entity of the cellularnetwork (preferably distinct from the second base station), a datatransmission configuration in respect of the second base station. Inparticular, this data transmission configuration is preferably based onone or more of: a characteristic of service data for transmission to theat least one mobile terminal; a parameter of an interface between thefirst and second base stations; a characteristic of the second basestation; and a state of a radio interface between the second basestation and the at least one mobile terminal. A data transmissionconfiguration (which may be a form of resource allocation or management)may comprise one or both of: a configuration of an interface between thenetwork entity (or the first base station) and the second base station;and a configuration of an interface between the second base station andthe mobile terminal. The management may be in terms of data quantityand/or rate, data allocation, physical/radio resource allocation or acombination of these parameters. Optionally, the method furthercomprises receiving information about the service data at the networkentity.

The method may comprise allocating, at a network entity of the cellularnetwork (preferably distinct from the second base station), at leastsome service data for transmission by the second base station. Inparticular, the service data is preferably allocated based on: a latencyof an interface between the network entity and second base stations; anda latency tolerance of the service data.

Preferably, no service data is allocated for transmission by the secondbase station if a transmission buffer state for the second base stationis at least a threshold level.

The method may also include: receiving the service data at the networkentity; and communicating at least some of the service data from thenetwork entity to the second base station based on the determinedallocation.

The method may comprise determining, at a network entity of the cellularnetwork (preferably distinct from the second base station), a datatransmission configuration in respect of the second base station. Inparticular, this data transmission configuration is preferably based on:an indication of an amount of data and/or resources for transmission tomobile terminals without carrier aggregation functionality being servedby the second base station; and an indication of an amount of dataand/or resources for transmission to mobile terminals with carrieraggregation functionality being served by the first base station.

Preferably, the step of determining comprises identifying an amount ofdata and/or resources for transmission by the second base station to theat least one mobile terminal.

Preferably, the step of identifying an amount of data and/or resourcesfor transmission by the second base station to the at least one mobileterminal is performed such that the second base station has capacity totransmit data to mobile terminals without carrier aggregationfunctionality being served by the second base station.

Preferably, the step of determining is further based on one or more of:a characteristic of service data for transmission to the at least onemobile terminal at a network entity of the cellular network; a parameterof an interface between the first and second base stations; acharacteristic of the second base station; and a state of a radiointerface between the second base station and the at least one mobileterminal.

Preferably, the steps of allocating and determining are carried out atthe same network entity.

Preferably, the network entity is the first base station (a masterand/or macro base station, as opposed to the second base station that istypically secondary and/or small). Optionally, the step of determiningcomprises identifying an amount of data for transmission by the secondbase station to the at least one mobile terminal. Specific details ofthe implementation will be discussed below, first with regard to flowcontrol (especially with reference to architecture 3C that was notedabove) and then in respect of scheduling.

Referring next to FIG. 11, there is shown a flow chart for flow controlof inter-eNB carrier aggregation data traffic. Flow control is not aspecific problem for architecture 1A, so this need not be implementedunless architecture 3C is selected. For flow control, a number ofparameters are considered: latency of the network interfaces (especiallythe Xn interface); buffer status of the SeNB; and delay tolerance of thetraffic. These will now be considered.

In general terms, the step of determining a resource allocation for thesecond base station may comprise determining an allocation of resourcesfor transfer between the network entity and the second base station.This may be termed flow control.

The MeNB is made aware of the Xn interface latency to decide which typeof data to be sent to the SeNB. If the latency of Xn interface is high,the MeNB would tend to forward delay tolerant data only to the SeNBwhereas if the latency is low the MeNB could decide to forward somenon-delay tolerant data. Nonetheless, the priority would be for the MeNBto transmit such type of data.

More generally, the parameter of an interface between the first andsecond base stations may comprise a latency of the interface. Then, thestep of determining may comprise allocating at least some of the servicedata for transmission by the second base station based on the latency ofthe interface. Additionally or alternatively, the characteristic of theservice data may comprise a latency tolerance. Then, the step ofdetermining may comprise allocating at least some of the service datafor transmission by the second base station based on the latencytolerance of the service data.

Flow control may be improved by the SeNB sending its buffer status tothe MeNB. The MeNB would decide how much data it should forward theSeNB. This may prevent the SeNB buffer to be overloaded and also reducesthe time needed by SeNB to request new data from the MeNB after itsbuffer is emptied.

In general terms, the characteristic of the second base station maycomprise a transmission buffer state. Then, the step of determining maycomprise allocating no service data for transmission by the second basestation (which may be understood as communicating no service data overan interface between the network entity and the second base station) ifthe transmission buffer state is at least a threshold level. Conversely,the method may comprise allocating at least some service data fortransmission by the second base station if the transmission buffer stateis less than the threshold level.

Another aspect of resource allocation concerns scheduling. In generalterms, the step of determining a resource allocation for the second basestation may comprise determining an allocation of resources fortransmission of service data by the second base station. This may betermed scheduling.

More specifically, the step of determining may comprise identifying anamount of data for transmission by the second base station to the mobileterminal.

Referring next to FIG. 12, there is shown a flow chart for configuringscheduling for inter-eNB carrier aggregation data traffic. Forscheduling, two approaches are proposed.

1. The eNBs involved in inter-eNB carrier aggregation may both fall backto a generic or simple, but efficient scheduling algorithm like theproportional fair scheduler where minimal information is exchangedbetween the eNBs like the past throughput of Rel-12 UEs, simply toprovide fairness to Rel-8 UEs.

2. An alternative approach is for the MeNB (or other network entity) totake full control of the scheduling of Rel-12 UEs on both eNBs. The SeNBwould send the MeNB its channel and load condition and the MeNB decideswhich resources should be used to schedule Rel-12 UEs on the SeNBcarrier, based on the information it receives and the traffic intendedto be forwarded to the SeNBs (the latter may only be possible inarchitecture 3C).

More generally, the step of determining comprises schedulingtransmissions from the second base station to the at least one mobileterminal. Optionally, the second base station serves at least one othermobile terminal (which may or may not use carrier aggregation). Then,the method may further comprise scheduling, at the second base station,transmissions from the second base station to the at least one othermobile terminal. Thus, resources for the transmissions from the secondbase station to the mobile terminal using carrier aggregation may beallocated at a network entity distinct from the second base station(such as the first base station). However, resources for thetransmissions from the second base station to other mobile terminals maybe allocated at the second base station.

Optionally, the characteristic of the second base station may comprise atraffic load on the second base station. The state of a radio interfacebetween the second base station and the at least one mobile terminal maycomprise one or more radio channel conditions, one or more radio linkquality parameter and/or a radio link performance parameter.

The characteristic of the second base station may comprise an indicationof an amount of data and/or resources for transmission to mobileterminals being served by the second base station of a second type (forinstance, without carrier aggregation) functionality and/or anindication of an amount of data and/or resources for transmission tomobile terminals of a first type (for example, with carrier aggregationfunctionality) being served by the first base station. In other words,information is provided by one or both eNBs about the quantity of datapreviously transmitted or intended for transmission (or resourceallocation used or intended for use) to Rel-12 UEs and/or Rel-8 UEs. Insome embodiments, the step of identifying an amount of data and/orresources for transmission by the second base station to the at leastone mobile terminal is performed such that the second base station hascapacity to transmit data to mobile terminals of the second type(without carrier aggregation functionality) being served by the secondbase station. In other words, the resource allocation to Rel-12 UEs atthe SeNB may be limited in order to ensure fairness to Rel-8 UEs.Additionally or alternatively, the network entity may be configured suchthat the first base station only allocates resources for transmission tomobile terminals of the first type.

In the preferred embodiment, especially when the network entity is thefirst base station, the step of receiving information about the servicedata comprises receiving the service data at the network entity. Then,the method may further comprise communicating at least some of theservice data from the network entity to the second base station based onthe determined resource allocation.

The method may be implemented by means of a computer program, which willcause the steps to be carried out when operated by a processor (or otherlogic). The computer program may be stored on a computer readablemedium. In another aspect, there may be provided a network entity of acellular network, configured to manage resources for service delivery toat least one mobile terminal using carrier aggregation across first andsecond base stations of the cellular network in accordance with themethod as described herein. The network entity may have structuralfeatures (such as respective components, modules or parts) configured toprovide the functionality associated with any of the steps discussedherein. The network entity is preferably the first base station,although it may be the second base station in some embodiments, part ofanother known network entity or a new network entity.

Any combination of specific features may be provided from any of theaspects discussed above, even if that combination is not explicitlydisclosed. Moreover, any part or combination of parts of this aspect maybe combined with any other aspect discussed herein.

1. A method for deciding on the activation of carrier aggregation acrossfirst and second base stations of a cellular network for delivering aservice to a mobile terminal, on the basis of a combination of aplurality of parameters, at least one parameter being associated with aperformance of the cellular network, at least one parameter beingassociated with a Quality of Service requirement of the service, atleast one parameter being associated with a state of the mobile terminaland/or a subscriber associated with the mobile terminal and, at leastone parameter being associated with a radio link between the mobileterminal and the first base station and/or second base station.
 2. Themethod of claim 1, wherein the at least one parameter associated withthe performance of the cellular network comprises an indication oflatency for communication between network entities of the cellularnetwork, the method further comprising: deciding to activate carrieraggregation if the indication of latency is less than a threshold value.3. The method of claim 1, wherein the at least one parameter associatedwith the Quality of Service requirement of the service comprises one ormore of: a latency requirement of the service; and a minimum bit raterequirement of the service.
 4. The method of claim 3, furthercomprising: deciding to activate carrier aggregation if the latencyrequirement of the service is at least a threshold delay tolerancelevel.
 5. The method of claim 1, wherein the at least one parameterassociated with a state of the mobile terminal comprises one or more of:a mobility state; a quality of service state; a battery state; and atransmission power back-off state.
 6. The method of claim 5, wherein theparameter associated with a mobility state is based on one or more of:Doppler information from a mobile terminal transmission; a rate ofhandover between base stations for the mobile terminal; a time durationof attachment of the mobile terminal to a base station; and a locationfor the mobile terminal.
 7. The method of claim 5, wherein the qualityof service state for the mobile terminal indicates a maximum delaytolerance for the mobile terminal, the method further comprising:deciding to activate carrier aggregation if the maximum delay tolerancefor the mobile terminal is at least a threshold delay tolerance level.8. The method of claim 5, wherein the parameter associated with amobility state indicates whether the mobile terminal is nomadic, themethod further comprising deciding to activate carrier aggregation ifthe mobile terminal is nomadic.
 9. The method of claim 5, furthercomprising: receiving the parameter associated with the battery state atthe cellular network from the mobile terminal; and deciding to activatecarrier aggregation if the parameter associated with the battery stateindicates that the battery power level is at least a threshold level ordeciding not to activate carrier aggregation if the parameter associatedwith the battery state indicates that the battery power level is lessthan a threshold level.
 10. The method of claim 5, wherein thetransmission power back-off state indicates a transmission powerback-off associated with carrier aggregation activation, the methodfurther comprising: assessing a throughput parameter for carrieraggregation activation based on the indicated transmission powerback-off; and deciding to activate carrier aggregation if the assessedthroughput parameter is at least a threshold level.
 11. The method ofclaim 1, wherein the at least one parameter associated with aperformance of the cellular network comprises a parameter based on anassessment of a change in throughput due to carrier aggregationactivation relative to a change in transmission overheads due to carrieraggregation activation.
 12. The method of claim 11, further comprisingdeciding to activate carrier aggregation if the assessment indicates anincrease in throughput due to carrier aggregation activation relative toa change in transmission overheads due to carrier aggregationactivation.
 13. The method of claim 1, wherein the step of deciding onthe activation of carrier aggregation is based on a weighted measure ofa plurality of the parameters.
 14. A computer program product having anon-transient computer readable medium having stored thereon executablecode that, when executed by a processor is configured to carry out themethod of claim
 1. 15. A network entity of a cellular network,configured to set an activation state for carrier aggregation based on adecision made in accordance with the method of claim 1.